Stainless steel is tough, corrosion-resistant, and notorious for chewing up drill bits. Success at drilling stainless steel comes down to the right bit, slow speed, and steady pressure rather than brute force.
Why Stainless Is Challenging
Stainless steel work hardens, which is the heart of the problem. If the bit rubs instead of cutting, the surface hardens under the tip and becomes nearly impossible to penetrate. Heat is the enemy because it both dulls the bit and hardens the metal in a vicious cycle. The whole technique is built around cutting cleanly from the first contact and keeping temperatures down so the material never gets a chance to harden ahead of the edge.
Choose the Right Bit
Bit selection makes or breaks the job. For most stainless work, cobalt bits in the M35 or M42 grades are the standard choice because the cobalt is alloyed throughout the steel and holds an edge at high temperatures. Solid carbide bits cut stainless well too and excel in rigid setups such as a drill press where there is no wobble to chip the edge.
- Cobalt HSS: Tough, heat-resistant, and re-sharpenable, the everyday choice for stainless.
- Solid carbide: Extremely hard and ideal for machine setups with no play or flex.
- Sharp geometry: A well-ground point starts cutting immediately and resists work hardening.
Speed, Pressure, and Fluid
Run slow. Large diameters and hard stainless demand low RPM to control heat build-up. Apply firm, constant pressure so the bit always bites rather than skating across the surface. Use a generous amount of cutting fluid to cool and lubricate the edge, re-applying it as you go, and never let the bit spin in place without advancing into the metal.
Step-by-Step Technique
Centre punch your mark so the bit cannot wander at the start. Drill a pilot hole first for larger diameters, keep the drill perpendicular to the surface, and maintain steady downward force throughout. Clear the chips regularly so they do not pack the flutes, and watch the colour of the swarf. If you see blue chips or smell burning, you are running too fast, too dry, or both, and should back off immediately.
Protect the Bit and Yourself
Let the bit cool naturally rather than repeatedly quenching hot HSS, which can cause micro-cracks. Wear eye protection and gloves, secure the workpiece in a vice, and watch for sharp swarf that can slice a bare hand. Quality American-made cobalt bits reward this careful approach with clean holes and long service life.
